In the medical field it is often required that a medical practitioner manipulate devices within a body cavity residing in a patient. In some cases, undesirable matter may exist or become lodged within the cavity and must be removed by the practitioner. At times, accumulation of the matter may reduce or cut off the flow of fluid, such as blood, and other essential components through the body cavity.
Some procedures for removing undesirable matter involve the challenging operation of maneuvering a cutting device within small confines of interior body cavities. In order to lead the cutting device to the site for removal of the matter, it must be routed through various internal structures, and the path through the body to the removal site may be tortuous. Usually, the cutting device is coupled to or otherwise associated with various devices, such as a drive shaft, guide wire, catheter(s), etc. that may guide the cutting device to the removal site.
One application for a cutting device is to remove atherosclerotic obstructions and partial obstructions. The use of rotating cutter assemblies is an established therapeutic intervention, and many different atherectomy methods and devices have been conceived and developed. Many of these systems involve placement of a guide catheter, a guidewire and a cutting device in proximity to an obstruction or partial obstruction in a blood vessel and then advancing and rotating the cutting device to cut or ablate the obstruction.
The following U.S. patents describe many types and specific features of devices for removing matter, which may be useful in atherectomy procedures: U.S. Pat. Nos. 4,898,575; 5,127,902; 5,409,454; 5,976,165; 5,938,670; 5,843,103; 5,792,157; 5,667,490; 5,419,774; 5,417,713; 4,646,736; 4,990,134; 4,445,509; 5,681,336; 5,695,507; 5,827,229; 5,938,645; 5,957,941; 5,019,088; 4,887,613; 4,895,166; 5,314,407; 5,584,843; 4,966,604; 5,026,384; 5,019,089; 5,062,648; 5,101,682; 5,112,345; 5,192,291; 5,224,945; 4,732,154; 4,819,634; 4,883,458; 4,886,490; 4,894,051; 4,979,939; 5,002,553; 5,007,896; 5,024,651; 5,041,082; 5,135,531; 5,192,268; 5,306,244; 5,443,443; and 5,334,211. These U.S. patents are incorporated by reference herein in their entireties.
Despite the varied approaches to the systems and methods exemplified by the U.S. patents cited above, many challenges remain in providing systems and methods for removing material from a lumen, such as a blood vessel, safely and reliably and without causing complications. The safety and reliability of the system is manifestly critical.
The cutting device must not damage delicate beneficial material, such as the walls of a structure or other healthy tissue, which often surrounds the unwanted matter. Thus, it is important for a cutting device to separate the unwanted matter from the beneficial material in a safe manner that is not so aggressive as to damage the beneficial material. Much attention is required in designing such a cutting device that has an optimal cutting surface and material removal mechanism.
Some special devices are designed to ablate unwanted matter without harming beneficial material by a method known as differential cutting. Differential cutting is based on the observation that oftentimes the unwanted matter located in the cavity is rigid and has a less elastic quality than the beneficial material of the body cavity. Generally, the beneficial material, such as the wall of a blood vessel wall, has a shear modulus of elastic stiffness that is a relatively low value. As a result, when a blade that is designed for differential cutting contacts the beneficial material, the material becomes deformed at the point of contact and large shear stresses in the beneficial material are not exerted. By comparison, the unwanted matter is generally more rigid and has a higher value of shear modulus of elastic stiffness. Harder material is not able to deform when contacted by the differential cutting blade, and shear stresses are consequently exerted on the more rigid material. In this manner, fragments of the harder, undesirable matter are cut away by differential cutting blades, while the more elastic, beneficial material is unharmed.
Various cutting devices have been proposed that utilize differential cutting principles. U.S. Pat. No. 4,445,509 describes differential cutting in the context of an atherectomy device. Some differential cutting devices have particular features to allow for differential cutting, such as the use of diamond grit on a cutting surface. This diamond grit surface forms random angles of attack and creates random cutting characteristics at various points of contact with the target undesired matter. In using diamond grit cutting devices, when applying increased depth of force of the device into the target matter to be removed, there is a greater risk of cutting into the supporting beneficial material in proximity to the target undesired matter. Thus, these prior devices require extreme caution in use in order to avoid cutting beneficial material.
One of the particular challenges of removing matter from the interior of lumens is that the drive and cutter assemblies must be small enough and flexible enough to travel over a guidewire to a desired material removal site, such as the site of an obstruction or occlusion. Yet, the drive and cutter assemblies must be large enough and have structural integrity sufficient to operate reliably and effectively to cut or scrape the obstruction. Additionally, removal of the debris from the material removal site using an aspiration system is generally desirable. The drive and cutter assemblies therefore desirably incorporate a debris removal system as well.
The size and consistency of the material comprising an obstruction are frequently not well characterized prior to introduction of the material removal device. Thus, although devices and cutters having different sizes and properties may be provided, and may even be interchangeable on a material removal system, it is difficult to ascertain which combination of features is desired in any particular operation prior to insertion of the device. The use of multiple cutter assemblies having different properties during a materials removal operation is inconvenient at best, since it requires removal of each independent device and interchange of the cutter assemblies, followed by reinsertion of the new cutter assembly, or of a new device entirely. Interchange and reinsertion of cutter assemblies is time consuming and generally deleterious to the health and condition of the patient undergoing the procedure.
Many different types of expandable cutters have been conceived in an effort to provide a cutter having a small diameter profile that may be conveniently delivered to and removed from the site of the desired material removal, and that is expandable at the site to provide a larger diameter cutter. The following U.S. patents disclose various approaches to expandable cutter assemblies: U.S. Pat. Nos. 5,540,707; 5,192,291; 5,224,945; 5,766,192; 5,158,564; 4,895,560; 5,308,354; 5,030,201; 5,217,474; 5,100,425; and 4,966,604. These U.S. patents are incorporated by reference herein in their entireties.
Although numerous approaches to cutter assemblies have been developed, there is still a need for a cutter assembly that is conveniently navigable to the material removal site and that that removes matter of different types in a safe and effective manner, without harming surrounding beneficial material.